Recently, in respect of a variety of electric and electronic apparatuses, reduction in size, thickness and weight and multi-functionalization are progressing rapidly. Particularly in the fields of cellular phones, laptop computers, digital cameras and the like, a demand for reduction in size and thickness as well as multi-functionalization is becoming very strong.
These types of electric and electronic apparatuses are produced incorporating a large number of electric and electronic components of various kinds, including circuit boards, where the electric and electronic components need to be electrically connected to each other.
A variety of methods are carried out for such connection.
For example, as a method for surface-mounting a semiconductor device onto a circuit board, an ACF connection method is known, in which an anisotropic conductive film is disposed between pads of a circuit board and pads of a semiconductor device, and then the whole is subjected to hot-pressing and bonding to electrically connect the circuit board and the semiconductor device. There are also known a method in which a semiconductor device with solder-bumps formed at pads is placed on a circuit board such that the solder-bumps are located on pads of the circuit board, and the whole is subjected to a reflow process; and a flip-chip method which is a variant of this method. There is also a method in which pads of a mounted component are wire-bonded to pads of a circuit board.
Any of these methods requires a special apparatus for connecting work, and once a connecting member is connected, it cannot be detached. Thus, when some circuit component needs to be replaced due to a design change or some connecting member needs to be replaced due to a failure, replacement of such circuit component or connecting member is very difficult. Thus, even when the other components are in order, the whole module has to be scrapped after all. In other words, in these connection methods, repair of each component is very difficult.
In the ACF connection method, the pitch between pads can be narrowed to 40 μm or so, and the height of a connection structure can be reduced to 100 μm or less. Although the ACT connection method thus relatively contributes to reduction in height of the connection structure and space-saving, the connection structure formed has drawbacks such that connection reliability is low, that a large current is not allowed to flow through, and that noise level is high. Thus, the connection structure formed by the ACF connection method is enough for practical use in consumer liquid-crystal modules through which only a small current flows and whose usage environment is not hard, but cannot serve for general uses including industrial uses.
In the connection method using the reflow process, if the pitch between bumps is narrowed to 150 μm or less, a short circuit can form between bumps due to melted solder. Thus, multi-pin formation is restricted. Meanwhile, in the wire-bonding connection method, portions at which wires are bonded are not very high in mechanical strength and vulnerable to external forces. Further, wire-bonding connection structure is inferior to, for example connection structure formed by the flip-chip method or the reflow process in respect of space-saving, since curved wires are bonded to the outside of a mounted component.
In any of these connection methods, connecting members form a permanent connection and do not allow repetition of a connecting operation. Further, if repair or change of a circuit is attempted forcibly, it results in breaking and scrapping the circuit partially or totally.
There is a connector structure in which an electrical connection between components is formed by mechanically engaging male and female connectors. This allows connecting members to be attached and detached from each other, repeatedly. There are actually used, for example an FFC connector structure in which, into female connectors mounted on a circuit board in a row, male connectors formed likewise in a row at an end of a flexible substrate are directly inserted; a pair connector structure in which, into female connectors mounted on a circuit board normally in two rows, male connectors formed likewise in two rows at an end of a flexible substrate are fitted; and a pin grid array connector structure which is a variant of the pair connector structure and in which the connecting terminals of male and female connectors are arranged in a grid-like array.
Use of such connector structure has an advantage that it allows repair. Specifically, since the components are detachably connected, even if some component goes out of order, it can be detached and replaced with a new component.
However, since the male and female connectors forming such connector structure, particularly the female connectors are normally fabricated from metal sheets using dies, the possibility of producing fine male and female connectors with high accuracy is limited. Thus, it is quite difficult to reduce the height of the connection structure in this connector structure.
For example, in the FFC connector structure, the height of the connection structure is normally 1 mm or greater. The minimum pitch between connecting terminals is 0.3 mm or so, and the connecting terminals are arranged in a row at one end. When the number of pins becomes 40 or greater, limitations on circuit design increase and actual inserting and pulling-out operations become difficult.
In the pair connector structure, the height of the connection structure is normally 1.3 mm or greater, and the minimum pitch is 0.5 mm or so. Although the connecting terminals can be arranged in two rows, when the number of pins becomes 60 or greater, limitations on circuit design likewise increase and actual inserting and pulling-out operations become difficult. Also the cost of producing the connectors increases.
The pin grid array connector structure can include an increased number of pins and is suited for space-saving. Meanwhile, it is difficult to reduce the pitch to less than 2 mm, and it is also difficult to reduce the height of the connection structure to less than 4 mm. Further, the cost of the pin grid array type connector structure is high, which hinders the application of this structure to general uses.